Internal combustion engines, particularly diesel engines, often include a boosting system to increase the pressure of the combustion air. The boosting system may include a turbocharger, which includes a compressor actuated by a turbine that is powered by a flow of exhaust gas from the engine. As is well known, the turbocharger lags behind the operation of the engine until the flow of exhaust gas through the turbine is sufficient to operate the compressor to pressurize the combustion air. Alternatively, the boosting system may include a supercharger, which is mechanically coupled to the engine, typically through a clutch. Because the supercharger is mechanically coupled to the engine, the supercharger is capable of operation almost immediately after the engine starts. However, the mechanical linkage between the supercharger and the engine draws power from the engine to operate the supercharger, thereby reducing the efficiency of the engine.
The boosting system may include both the turbocharger and the supercharger disposed sequentially in series. In such a boosting system, the supercharger is used when the turbocharger is operating inefficiently, such as during startup and initial acceleration. Once the turbocharger is operating efficiently, such as during high speed operation of the vehicle, the clutch disengages the supercharger from the engine to eliminate the power draw required to operate the supercharger. Because the turbocharger is powered by the flow of exhaust gas, operation of the turbocharger does not draw power from nor reduce the efficiency of the engine.